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Hip Replacement
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Ultra-high molecular weight polyethylene is a polymer. The word polymer comes from the Greek word polumeres, which means having many parts. Thus, a polymer is simply many units of atoms that are bonded together to form a long chain. In the case of Ultra-high molecular weight polyethylene (UHMWPE), many polyethylene chains that are extremely long are bound together to form one UHMWPE chain. UHMWPE has a greater toughness and wear resistance than regular polyethylene, but it can wear down in a process that is known as oxidation. During oxidation, oxygen reacts with chain ends of the polyethylene that do not have enough electrons. When the oxygen bonds to the free ends of the polyethylene chains, other molecules that would normally bond to the polyethylene chain cannot bond to it, and thus the material is degraded or weakened. When a stress is applied to the oxidized UHMWPE, it will wear at a rate that is faster than normal.
When UHMWPE particles are produced from the articulating motion of implant, the particles are foreign to the body, and as a result the body reacts to them in an unusual way. When the body normally reacts with a foreign material that is in the body during acute inflammation, which is short-term inflammation, phagocytosis occurs. During phagocytosis, a macrophage travels to the foreign body via the white blood cells and attempts to "eat", or dispose of the foreign material.
When phagocytosis is not successful, and the macrophages cannot dispose of the foreign matter in the body, acute inflammation progresses to chronic, or long term inflammation. Sometimes during chronic inflammation, the white blood cells induce self-injury to the body. This is known as an autoimmune reaction.
Unfortunately, as stated above, the method used to sterilize these prostheses is well noted for causing oxidation.
The degradative effect of irradiation on polyethylene and other polymers has been known for many years. Experts have described the mechanisms behind the oxidative degradation of polymers, noting that ionizing radiation interacted with long chain polymers, forming free radicals. In an example, polyethylene was shown to degrade to form a hydrogen radical and a polyethylene radical. The chain scission which was caused in this reaction led to two possible outcomes. Either cross-linking could occur between the polymeric radicals, or, in the presence of oxygen, oxidation of the polymeric chains could occur. In the former case, polymeric chains effectively became longer, and a network structure was formed. In the latter oxidation situation, the polymeric radical could be terminated through the addition of, for example, one of the hydrogen radicals or an oxidation free radical. This termination would lead to lowering of the molecular weight.
Class Action lawsuits have been filed against Johnson & Johnson and Depuy arising out of the alleged failure of the their allegedly defective Ultra High Molecular Weight polyethylene knee joint and hip replacement prostheses. According to the allegations in the complaints, the prostheses at issue have been sterilized with gamma radiation, resulting in premature failure of the product.
If you or a member of your family has a Johnson & Johnson/Depuy Knee Prosthesis made of Ultra High Molecular Weight Polyethylene, you may have a claim. To ensure that you receive just compensation, you should consider contacting an attorney with experience handling this type of case.
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